Electricity (P4)

Question 1

What is Ohm’s law

Answer 1

The voltage across a conductor is directly proportional to the current flowing across us provided all physical conditions stay the same

Question 2

What is the rule linking resistance and I-V graphs?

Answer 2

The steeper the gradient of the line, the less the resistance. Because R=v/i

Question 3

equation linking charge current and time

Answer 3

Charge flow (Q) = Current (I) x time taken. (Q=It)

Question 4

equation linking pd, current and resistance

Answer 4

Potential Difference (V) = Current (I) x Resistance (R) 
(V=IR)

Question 5

what is the unit of measurement for Resistance

Answer 5

Ohms

Question 6

what is the unit of measurement of current

Answer 6

Amperes (amps)

Question 7

what is the unit of measurement for potential difference

Answer 7

Volts

Question 8

what is the unit of measurement for charge

Answer 8

Coulombs

Question 9

What is the unit of measurement of time taken

Answer 9

seconds

Question 10

what is the unit of measurement of energy transferred

Answer 10

Joules

Question 11

What is the unit of measurement of Power?

Answer 11

Watts

Question 12

How temperature effects the resistance of a thermistor

Answer 12

As the temperature increases, the resistance decreases

Question 13

How is an ammeter connected in a circuit

Answer 13

In series

Question 14

how is a voltmeter connected in a circuit

Answer 14

in parallel

Question 15

Define electric current

Answer 15

The rate of flow of electric charge

Question 16

what is direct current

Answer 16

the movement of charge through a conduction in one direction only

Question 17

what is alternating current

Answer 17

an electric current that regularly changes its direction and size

Question 18

Equation linking potential difference, energy transferred and charge

Answer 18

Energy transferred (E) = Potential difference (V) x charge (Q)
E=VQ

Question 19

How resistance affects current

Answer 19

The greater the resistance across a component, the smaller the current that flows through it, for a given potential difference across the component

Question 20

How length of wire affects resistance

Answer 20

The longer the wire, the greater the resistance as electrons collide with more ions as they pass through. Relationship between wire length and resistance is proportional

Question 21

How thickness of wire affects resistance

Answer 21

Relationship between resistance and the area of a cross section of a wire is inversely proportional. The resistance of a thin wire is greater than the resistance of a thick wire as there is less space so fewer electrons can carry the current through it

Question 22

How Resistance changes in a filament lamp

Answer 22

As current flows through the lamp, it transfers some energy to the thermal store of the filmament so the bulb heats up. Resistance increases with temperature as the metal ions vibrate with a higher amplitude so the number of collisions between metal ions and electrons increases. So as the current increases, the filament lamp heats up more and resistance increases

Question 23

How resistance changes in diodes

Answer 23

The resistance depends on the direction of the current. Current will only flow through a diode in one direction and the diode has a very high resistance in the reverse reaction

Question 24

How can you calculate the resistance from an I-V characteristic

Answer 24

The gradient = the resistance and the steeper the gradient, the less the resistance as R=V/I

Question 25

What is a Light Dependant Resistor

Answer 25

A resistor that is dependant on the intensity of light, in bright light the resistance falls so the resistance is highest in the dark. (LURD)

Question 26

What is a thermistor

Answer 26

a temperature dependant resistor. as temperature increases, the resistance decreases (TURD)

Question 27

what happens to potential difference in series circuits

Answer 27

the total potential difference of the supply is shared between various components

Question 28

What happens to current in a series circuit

Answer 28

The current that flows through all the components is the same everywhere in a circuit

Question 29

What happens to total resistance in a series circuit and why

Answer 29

The total resistance of two components is just the sum of their resistances. This is because adding a resistor in series, the resistors have to share the total potential difference so the pd across each resistor is lower so the current is also lower. the current in a series circuit is then reduced when resistance is added so the total resistance increases

Question 30

What happens to potential difference in parallel circuits

Answer 30

the potential difference is the same across all components as all components get the full source of pd

Question 31

what happens to current in parallel circuits

Answer 31

the total current flowing around the circuit is equal to the total of all the currents through the separate components

Question 32

What happens to resistance in parallel circuits

Answer 32

if you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors. so adding a resistor in parallel reduces the total resistance

Question 33

Why does this happen to resistance in a parallel circuit

Answer 33

both resistors have the same potential difference which means the pushing force making the current flow is the same for each resistor. any adding a loop the current has more than one direction to go and this increases the current that can flow around the circuit. Using V=IR, an increase in current means a decrease in total resistance

Question 34

What happens when a polythene rod is rubbed with a cloth duster

Answer 34

the electrons move from the duster to the rod and this causes the rod to become negatively charged and the cloth to become positively charged

Question 35

What happens when an acetate rod is rubbed with a cloth duster

Answer 35

electrons move from the rod to the duster and the rod becomes positively charged and the duster becomes negatively charged

Question 36

Rules for drawing electric field lines

Answer 36

1. direction of the arrow goes from positive to negative to show the way a positive charge would be pushed 2. the closer together the arrows, the stronger the field and the greater the force experienced by charges in the field

Question 37

How are sparks caused

Answer 37

When there is a high potential difference between a charge object and the earth there is a strong electric field which causes electrons in the air to be removed (ionisation) which makes air more conductive so a current can flow through it which is the spark